During laparoscopic surgery, one or more small incisions are formed in the skin of a patient and a trocar assembly is inserted through the incision to form a pathway that provides access to an internal body cavity, such as the patient's abdomen. The trocar assembly is used to introduce various instruments and tools into the abdomen, as well as to provide insufflation that elevates interior walls of the abdomen.
A trocar assembly generally includes a housing, a cannula that extends from the housing, and an obturator that can be inserted into the housing and the cannula. To set the trocar assembly for a surgical operation, the obturator is extended through an interior lumen of the cannula, at which point the obturator may penetrate the patient's skin to access the abdominal cavity. To penetrate the skin, the distal end of the cannula is placed against an incision in the skin and pressure is applied to the proximal end of the trocar to force the sharp point of the obturator through the skin until it enters a targeted location in the abdominal cavity. The obturator can then be withdrawn, leaving the interior lumen of the cannula as a path to access the abdominal cavity from outside the body.
The trocar housing is attached to the proximal end of the cannula and defines a working chamber with an open distal end in communication with the interior lumen of the cannula. Just as the interior lumen can receive the obturator, it is also sized to receive elongated surgical tools that are axially extended into and withdrawn from the cannula through the proximal end portion of the working chamber.
For surgical operations, a surgeon will normally use a 1:1 pairing of a trocar assembly and a surgical tool based on size (diameter). For example, if an 8 mm (diameter) surgical tool is required for an operation, a corresponding 8 mm (diameter) trocar assembly will normally be used. In robotic surgery, however, trocar assemblies and surgical tools do not always enjoy a 1:1 pairing. For example, 12 mm (diameter) trocar assemblies are typically used in robotic surgery, which enables use of 12 mm (diameter) surgical tools, such as a surgical stapler. For some procedures, however, an 8 mm or 5 mm (diameter) surgical tool may be required and will have to pass through the same 12 mm trocar assembly.
When the trocar assembly and surgical tool pairing is not 1:1, the tip (distal end) of the surgical tool is prone to various types of unintended motion, such as deflection, oscillation in place, and spring back oscillation. Unintended tip motion can lead to the instrument contacting or damaging tissues in a manner contrary to the intent of the surgeon. These events resulting from unintended motion can produce adverse clinical impacts. For instance, unintended lacerations or other tissue damage may require additional surgical intervention or even permanent tissue damage.